1. Field of the Invention
The present invention relates to an engine brake control system for a vehicle provided with a variable-speed V-belt drive.
2. Description of the Related Art
When the engine of a vehicle provided with a variable-speed V-belt drive including a drive pulley and a V belt, and a gear transmission is idling, the drive pulley of the variable-speed V-belt drive is set in a minimum working diameter and power cannot be transmitted from the drive pulley to the V belt even if the gear transmission is set for a speed other than neutral. Consequently, engine brake is scarcely effective. Another vehicle provided with an engine brake device and a variable-speed V-belt drive including a drive pulley measures the traveling speed of the vehicle by a traveling speed sensor, and engine brake device restricts the decrease of the working diameter of the drive pulley of the variable-speed V-belt drive to a predetermined minimum working diameter to make engine brake effective when the traveling speed is not lower than a predetermined traveling speed.
The former vehicle not provided with an engine brake device needs to be braked or stopped by a braking operation for operating a foot brake or a hand brake either during a forward traveling state or a reverse traveling state on a slope.
In the latter vehicle provided with the engine brake device, engine brake is effective when the traveling speed is not lower than a predetermined traveling speed and hence the frequency of braking operation while the vehicle is traveling a slope is reduced. However, if engine brake becomes effective regardless of the driver""s intention particularly while the vehicle is reversing, the driver is apt to feel an unpleasant feeling, which spoils comfortableness in riding on the vehicle.
Particularly, if engine brake becomes suddenly effective while a straddle-type all-terrain vehicle is reversing on a slope, the rider will feel like being pushed backward and is apt to feel an uncomfortable feeling because the seat of the straddle-type all-terrain vehicle is not provided with any backrest and a rider riding the straddle-type all-terrain vehicle is exposed.
Accordingly, it is an object of the present invention to improve the riding comfortableness of a vehicle while the vehicle is traveling a slop by making engine brake effective only while the vehicle is in forward travel.
Another object of the present invention is to facilitate the compact arrangement of sensors including a traveling speed sensor.
According to the present invention, an engine brake control system for a vehicle provided with a variable-speed V-belt drive including a drive pulley and a gear transmission disposed below the variable-speed V-belt drive with respect to a power transmitting direction comprises a traveling speed sensor for measuring the traveling speed of the vehicle, a traveling mode discriminating sensor for discriminating between a forward travel mode and a reverse travel mode, and an engine brake device capable of making engine brake effective by restricting the decrease of the effective diameter of the drive pulley while the vehicle is traveling at traveling speeds not lower than a predetermined traveling speed; wherein engine brake is made ineffective while the traveling mode discriminating sensor is providing a signal indicating the reverse travel mode.
When the engine is idling and the vehicle is in forward travel on a downhill, the vehicle is accelerated by gravity. Upon the increase of the traveling speed beyond a predetermined traveling speed, the decrease of the working diameter of the drive pulley of the variable-speed V-belt drive is restricted to hold the variable-speed V-belt drive in a power transmitting condition, so that engine brake is effective. On the other hand, when the vehicle is traveling down a downhill in a reverse travel mode, the traveling mode discriminating sensor detects the reverse traveling mode and the engine brake device makes engine brake ineffective. In this case, the vehicle is braked by operating a foot brake or a hand brake.
Preferably, in the engine brake control system according to the present invention, a detection rotor is attached to a rotating member which rotates in directions respectively corresponding to the forward travel mode and the reverse travel mode, the traveling mode discriminating sensor is disposed opposite to the detection rotor, and the detection rotor is provided with three or more projections arranged at unequal angular intervals.
The rotating direction of the detection rotor in the forward travel mode and that of the same in the reverse travel mode can be easily discriminated.
Preferably, in the engine brake control system according to the present invention, the traveling mode discriminating sensor and the traveling speed sensor are disposed so as to detect the rotation of an output shaft included in a gear transmission or a drive shaft connected by a bevel gear mechanism to the output shaft of the gear transmission.
Such arrangement of the traveling mode discriminating sensor and the traveling speed sensor facilitates mounting the traveling mode discriminating sensor and the traveling speed sensor on the vehicle.
Preferably, in the engine brake control system according to the present invention, the traveling mode discriminating sensor and the traveling speed sensor are disposed on the axially opposite sides, respectively, of the gear transmission.
Such disposition of the traveling mode discriminating sensor and the traveling speed sensor facilitates mounting the traveling mode discriminating sensor and the traveling speed sensor on the vehicle.
Preferably, in the engine brake control system according to the present invention, the traveling speed sensor is disposed near the outer circumference of a bevel gear mounted on the drive shaft, and the traveling mode discriminating sensor is disposed near an end of the output shaft opposite the other end of the output shaft on the side of the drive shaft.
Preferably, in the engine brake control system according to the present invention, the plurality of projections formed on the rotor have different circumferential lengths, respectively. Thus, false discrimination between a forward travel mode and a reverse travel mode can be prevented.